Long Lake
Polk County, WisconsinEutrophic
Long Lake sits at a C on the grading scale — not impaired, not pristine, with summer measurements that vary year to year. Clarity is the limiting factor — phosphorus is reasonable but suspended particles or algal cells keep water transparency below Wisconsin norms.
At a TSI of 51, Long Lake reads as eutrophic — nutrient-rich enough that summer algal growth and reduced clarity are expected, not unusual. A maximum depth of 17 ft puts Long Lake in the middle of Wisconsin's depth distribution. At 273 acres, Long Lake fits the Wisconsin median for monitored lakes, with partial shoreline records. Long Lake ranks 62 of 77 in Polk County — at the lower end of the locally monitored distribution.
An invasive species record — Banded Mystery Snail — has been logged at Long Lake; Wisconsin DNR maintains the official infested-waters list. Bass fishing is part of the appeal: the species list runs to 3, anchored by largemouth and/or smallmouth bass. Public access is available — the lake is on the Wisconsin DNR public-access list. The grade is based on limited monitoring — fewer than three independent measurement years contribute, so future updates may shift the letter.
Source: EPA Water Quality Portal sampling records, Wisconsin DNR Surface Water, last sampled 2025-09-23. Grade methodology: LakeGrade methodology.
Swimming Safety
Generally safe for swimming, moderate water quality
Water Quality Grade: C, Fair
Murky, only visible to about 5.9 ft. Phosphorus level: 26.1 µg/L. Trophic State Index: 51.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 5.9 ft | D |
| Phosphorus | 26.1 µg/L | B |
| Chlorophyll-a (Algae) | No data | |
| Trophic State Index (TSI) | 51 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 17 ft |
| Surface Area | 273 acres |
| Public Access | Yes |
Fish Species
Click a species to see all Wisconsin and Minnesota lakes where it is found.
→ Best fishing times for Long Lake (14-day solunar calendar)
→ Is it safe to eat fish from Long Lake? (mercury & PFAS guide)
→ Long Lake fishing regulations (limits, seasons, special rules)
Invasive Species
Water Quality Trend: ↑ Improving
Based on 7 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +0.604 m/yr | 7 |
| Phosphorus | ↑ Improving | -1.54 µg/L/yr | 6 |
Recreation & Access
Location
County Ranking
Ranked #62 of 77 lakes in Polk County
Cleaner Lakes Within 30 Miles
Long Lake holds Grade C. 5 nearby lakes hold higher grades.
- ADeer LakePolk County · 3.5 mi · Two grade letters higher (C → A)
- ALoveless LakePolk County · 1.1 mi · Two grade letters higher (C → A)
- ABalsam LakePolk County · 3.8 mi · Two grade letters higher (C → A)
- BLittle Bass LakePolk County · 2 mi · Higher grade (C → B)
- BRice LakePolk County · 3.5 mi · Higher grade (C → B)
Nearby Lakes in Polk County
More Wisconsin Lake Rankings
State Parks Near Long Lake
Other Grade C Lakes in Wisconsin
Eutrophic Lakes in Wisconsin
WI DNR Lake Profile
Authoritative data from the Wisconsin DNR LakePages. Monitored by volunteers since 1992. 2 stations on file (most recent sample 2025).
Fish Species (DNR-rated)
Data Sources
Water quality data from the EPA Water Quality Portal
Grading methodology based on Metropolitan Council standards
Fish and recreation data from Wisconsin DNR Lakes
Most recent sample: 2025-09-23
Monitoring stations: 1